Phase diagram of the Cu–Ni₃Al pseudo-binary system

Cu–Ni–Al alloys with a Ni to Al ratio of approximately 3.0 are of particular interest for the development of electrically conductive products; thus, investigating their phase behavior is essential for achieving specific properties in these materials. In this study, the phase diagram of the Cu–Ni₃Al pseudo-binary system was experimentally determined using cast and fully heat-treated Cu–Ni₃Al alloys with a wide range of compositions, via microstructural observation and different quantitative analyses. The Cu–Ni₃Al system undergoes a eutectic reaction Liquid ↔ α-Cu solid solution (Cu_ss) with an FCC structure +γ′-Ni₃Al with an ordered FCC L1₂ structure. As the combined Ni and Al (Ni₃Al) content increased, the microstructure transitioned from a single α-Cu_ss phase to two eutectic phases (α-Cu_ss and γ′-Ni₃Al), to a primary γ′-Ni₃Al phase and two eutectic phases, and to a single γ′-Ni₃Al phase. The solidus and liquidus temperatures increased with the (Ni+Al) content. The solid solubility of (Ni+Al) in the α-Cu_ss phase (C_(Ni+Al)) could be described by an Arrhenius-type equation (ln C_(Ni+Al) = 5.50 – 2637/T), indicating a significant temperature dependence. In contrast, the solubility of Cu in the γ′-Ni₃Al phase did not significantly decrease with the temperature. The phase diagram of the Cu–Ni₃Al system was constructed from these results. The phase diagram will be useful in the development of Cu–Ni–Al alloys with exceptional strength and electrical conductivity.